Photoreceptive membrane is maintained through shedding and renewal. The progress report describes the strategy of genetic dissection, utilizing transduction mutants to characterize turnover in photoreceptors of Drosophila. Autophagy proceeds as coated vesicles merge to multivesicular bodies (MVB's) which are attacked by lysosomes and degraded. The degradative pathway may also involve exocytotic shedding followed by phagocytosis. The study of membrane assembly is facilitated by a paradigm of carotenoid "replacement therapy" which was developed to optimize the investigation of insertion of new rhodopsin- containing membrane. The effects of light on shedding (a day night cycle and a treatment which reduces rhodopsin) will be determined. Rhodopsin levels can be correlated with ultrastructural aspects of membrane cycling in a multifaceted approach emphasizing microspectrophotometry (MSP), electron microscopy (EM) and genetic dissection. Per mutants having pervasive alterations on their biological clocks will allow Drosophila to add a new dimension to the growing literature on circadian effects in the retina. Shi, with a temperature sensitive endocytosis defect, is uniquely suited to dissect phenomena of autophagy. The Acid phosphatase negative (Acph-) mutant will be helpful in determining the cell biology of the degradative pathway through histochemical visualization of this lysosomal enzyme. Ocellar mutants will serve to test the expectation from research on Limulus that ocellar input influences turnover in the compound eye. Immunocytochemistry with anti-rhodopsin and anti-per antibodies will provide exciting avenues to explore the mechanisms of upkeep of the photoreceptor membrane. Rhodopsin insertion will be determined using autoradiography. Tunicamycin, which blocks rhodopsin synthesis, will also be useful in determining how assembly of photoreceptive membrane proceeds.